1. Field of the Invention
The invention relates to a method and system for imaging, diagnosing, and/or treating an area of interest in a patient's body.
2. Background of the Related Art
The use of less invasive, catheter-based, intravascular techniques has been developed over several decades and may be considered the preferred mode of treatment for those patients amenable to such treatment. Typically, intravascular procedures, such as angioplasty, atherectomy, and stenting, are preceded by a diagnostic procedure, such as angiography and in some cases IntraVascular UltraSonic (IVUS) imaging.
IVUS imaging can frequently provide additional diagnostic information over what is readily obtained using a fluoroscope and radio-opaque dyes as in angiography. This stems from the fact that geometric measurements are based on cross-sectional images not “shadow grams” as in single plane angiography and by virtue of the high contrast nature of the interaction of sound with tissue as opposed to the interaction of x-rays with tissues. Further, the angiogram requires the use of x-ray contrast agents that opacify the blood pool and therefore are not intended to examine the tissue in the vessel wall, but rather the path of the blood pool itself.
With almost all modern interventional catheter procedures, an interventionalist or operator first places a guidewire into a target anatomy or site, such as a vessel(s), artery, or other body cavity of diagnostic or therapeutic interest. The guidewire is used to navigate the target anatomy in the patient's body prior to the diagnostic or therapeutic catheter being inserted.
The placement of the guidewire is frequently the most difficult and time consuming part of the entire procedure. Consequently, once the guidewire has been advanced into the target anatomy, the interventionalist or operator does not want to lose the position of the distal end of the guidewire.
After the guidewire is in place, various diagnostic and therapeutic catheters, such as balloon catheters, stent deployment catheters, atherectomy catheters, IVUS catheters, and thrombectomy catheters, are “loaded” over the guidewire. The guidewire, so placed, serves as a rail along which catheters can be advanced directly to, and withdrawn from, the target site.
There are two basic categories of catheters that are used in conjunction with these guidewires. The first category of catheters is referred to as “Over-The-Wire” (OTW) devices. Catheters in the first category have a lumen that extends inside the entire length of the catheter into which a guidewire can be inserted. The second category of catheters is referred to as “RX” or “rapid exchange” (RX) catheters. In these catheters, the guidewire only enters into the catheter body near its distal end, instead of entering at the proximal-most end, and extends inside the catheter body to the distal most end of the catheter where it exits.
There are advantages and disadvantages to both designs. The OTW catheters allow easy exchange of guidewires should additional catheter support, from a stiffer guidewire, or a change in the shape or stiffness of the guidewire tip be necessary. The RX catheters allow the operator to more rapidly change from one catheter to another while leaving the guidewire in place, thereby preserving the placement of the guidewire distal tip, which may have been difficult to achieve. Although “standard” length (typically ˜190 cm) guidewires usually have a proximal extension capability built in (extending the overall length to ˜300 cm), the use of these accessories is cumbersome and can require two sterile operators.
Typically, ˜190 cm guidewires are required to span a vessel from the most distal anatomy that the interventionalist or operator wishes to treat to the point where the guide catheter, enters the patient's body. The entry point may be located, for example, at the femoral artery in a patient's groin, or on occasion, the radial artery in a patient's arm. If the catheter being loaded over the guidewire is an OTW catheter, the guidewire must be long enough so that the entire length of the OTW catheter can be slid over the proximal end of the guidewire and yet there remain some length of the guidewire exposed where it enters the patient's body. That is, the guidewire for an OTW catheter must be approximately twice as long as one that is to be used only with RX catheters, because it must simultaneously accommodate both the length inside the patient's body and the length of the OTW catheter. Further, the “threading” of the OTW catheter over the distal or proximal end of the guidewire is time consuming, and the added length of the guidewire can be cumbersome to handle while maintaining sterility.
Since the RX design catheters typically have the guidewire running inside them for only the most distal ˜1 cm to ˜30 cm, the guidewire employed need only have a little more than the required ˜1 cm to ˜30 cm after it exits the patient's body. While the loading of an ˜140 cm OTW catheter over an ˜280 cm to ˜300 cm guidewire is time consuming and tedious, loading the distal ˜10 cm of an RX catheter over a shorter guidewire is easily done.
However, OTW catheters tend to track the path of the guidewire more reliably than RX catheters. That is, the guidewire, acting as a rail, prevents buckling of the catheter shaft when it is pushed forward from its proximal end over the guidewire. RX catheters can, however, given a sufficiently wide target site, such as a sufficiently wide artery, and a sufficiently tortuous guidewire path, buckle as they are advanced along the guidewire by pushing on the proximal end of the catheter. In addition, when an RX catheter is withdrawn from a patient, the RX portion can pull on the guidewire and cause the guidewire to buckle near the point that it exits the proximal end of the RX channel.
There are advantages to both designs. However, when the path of the target anatomy, such as a vessel, that is to be imaged is not too tortuous and the location of the target imaging site is not too difficult to reach, the mono-rail or RX catheters are preferred.
Recently catheters and systems have been developed to visualize and quantify the anatomy of vascular occlusions by using IVUS imaging. IVUS techniques are catheter-based and provide real-time cross-sectional images of a target anatomy, such as a vessel lumen, diseased tissue in the vessel, and the vessel wall. An IVUS catheter includes one or more ultrasound transducers at or near the distal tip of the catheter by which images containing cross-sectional information of the vessel under investigation can be obtained. IVUS imaging permits accurate geometric measurements, visualization of the atherosclerotic plaques, and the assessment of various therapies and complications that may result.
Motor driven, mechanically steered IVUS imaging systems typically include an arrangement in which a single transducer near the distal end of the catheter is rotated at high speed (up to about 1800 rpm) to generate a rapid series of ˜360-degree ultrasound sweeps. This is exemplified by U.S. Pat. No. 4,794,931 to Yock, which is hereby incorporated by reference. Such speeds result in generation of up to about thirty images per second, effectively presenting a real time cross-sectional image of, for example, a diseased vessel or artery.
The transducer assembly is mounted on the end of a drive shaft that is connected to a motor drive at the proximal end of the catheter. Incorporated into the motor drive, or in some cases separate from the motor drive, is an angle encoder that records the angular position of the transducer assembly. The rotating transducer assembly is housed in a sheath that protects the vessel or artery from the rapidly spinning drive shaft. The IVUS imaging catheter is advanced to the region of interest using the guidewire RX technique to provide real-time cross-sectional images of the lumen and the vessel or arterial wall at the desired target site. The presence of a mechanically spinning imaging core in the center of the IVUS catheter prevents OTW versions of motor driven, mechanically steered IVUS catheters.
There is, however, a commercially available, electronically steered IVUS catheter that does not contain a central spinning imaging core that is amenable to either OTW designs or RX designs. Such a catheter and imaging system is disclosed in U.S. Pat. No. 4,917,097 Proudian, which is hereby incorporated by reference. The electronically steered IVUS catheters have a ring of ultrasonic transducers located at the distal tip of the catheters. Tiny electronic multiplexers located just proximal to the ultrasonic transducers are used to select a subset of the ultrasonic transducers. By selecting different sets of adjacent elements, the ultrasonic beam can be electronically rotated in practically any radial direction around the catheter.
U.S. patent application Ser. No. 11/053,141 (hereinafter the “'141 application”), which is hereby incorporated by reference, teaches a novel combined therapy and IVUS catheter that is neither electronically steered nor attached to an electric motor and spinning rapidly as in conventional commercially available products. The '141 application covers a manually rotated, OTW IVUS system whereby the operator sweeps out a complete image of, for example, a vessel or a sector of a vessel when needed by simply rotating the catheter with his or her hand. There are many advantages to such an approach; however, the apparatus as taught in the '141 application, due in part to its combined role in therapy, is not amenable to a rapid exchange design. The catheter described in the '141 application can, with the removal of the RF ablation antenna, be employed as a purely diagnostic device in a fashion analogous to all other commercially available IVUS devices.
In the '141 application, the entire catheter is rotated in order to sweep out an image, and there is no obvious way to make this type of device into an RX catheter. That is, because in an imaging application the entire shaft of the catheter is rotated frequently and if the guidewire were to enter the catheter body say ˜1 cm to ˜3 cm from the distal end of the catheter as in an IVUS RX design, the interventionalist or operator would be required to torque both the catheter body and the external length of the guidewire in order to make an image. Rotating the guidewire and the IVUS catheter frequently to make IVUS images would potentially damage the vessel wall and cause geometric distortions in the resulting image due to the increased wind-up and backlash at the distal end of the catheter.
In order to provide for the maximum utility of a manually steered IVUS system, there is a need for both an OTW version and a RX version of catheter depending on the particular application.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.